Lost in Translation

DOMINIC AKANDWANAHO

The phenomenon of antibiotic resistance has been on the rise in many countries worldwide. A 2011 article in the Economist attempts an explanation for the human behaviors that could be fueling this trend. For some diseases, like tuberculosis, the problem is, according to Dr.T.V.Rao, a professor at Travancore Medical College in India, “an emerging human concern”. Although global health efforts have made huge strides in the treatment of tuberculosis, data from the World Health Organization indicates that 8.9 million people fell ill with the disease in 2012. About 6% of those were infected by the multi-drug resistant strain Mycobacterium tuberculosis.

Evidence from the Javid Lab at Tsinghua University has shown that error in the process of protein synthesis for mycobacteria, the type of bacteria involved in tuberculosis, varies significantly under different environmental stress conditions and might be linked to phenotypic drug tolerance in these species (Javid et al.). Phenotypic drug tolerance, unlike genetic drug resistance, appears not to be transferable between generations of bacteria since it is not genetically encoded in the bacterial genome.

Specifically, phenotypic drug tolerance in different species of Mycobacteria appears to arise from an error in protein synthesis known as mistranslation. Mistranslation, as its name suggests, occurs when an amino-acid-coding fragment of the genome is translated into the incorrect amino acid. Such incorrect amino acid substitutions can modify a protein such that it is no longer susceptible to drug inhibition–that is, it will function even in the presence of a drug designed to disable it. If the connection between mistranslation and drug tolerance in Mycobacteria is indeed valid, then molecules that reduce bacterial mistranslation rates could play a role in fighting this kind of drug tolerance.

This summer, under the supervision of Prof. Babak Javid at his lab at Tsinghua University, I have been quantifying mistranslation rates in M. smegmatis cultured in test tubes. This bacterium is a close relative of M.Tuberculosis, making it a reliable model organism for this experiment. Moreover, our lab’s safety protocols make it impossible to work directly with M.tuberclosis since it is highly pathogenic. I am using a luciferase reporter system in M. smegmatis to characterize the rates at which single amino acid residues are mistranslated. The luciferase reporter system consists of a set of genes that produce a luminescent protein—the same kind of protein that makes fireflies glow on a summer evening. If I introduce mutations into fragments of the luciferase gene that interfere with the functioning of the luminescent protein, then I expect to no longer see luminescence. Any luminescence observed is attributed to mistranslation; an essential amino acid residue has been re-introduced at a key position where the mutated gene coded for a different residue. Essentially, an error during translation has occurred, partially restoring enzyme activity and thus luminescence. The firefly luciferase system has an extremely dynamic range, allowing for the detection of even minute activities. This makes it a very useful reporter of bacterial mistranslation rates.

The luciferase reporter system consists of a set of genes that produce a luminescent protein—the same kind of protein that makes fireflies glow on a summer evening.”

My summer project follows on from work started by Tianqi Leng, who recently graduated from Peking University. He showed that mistranslation rates vary in M.smegmatis under different stressors. Some of the conditions being investigated include temperature and the presence of an antibiotic and oxidative stress. Once we can get enough data about the changes in mistranslation rates in these different conditions, we can try to understand the mechanism of mistranslation to determine relevant targets for intervention.